GB342651A - Improvements in the manufacture of artificial filaments, threads & the like by wet spinning methods - Google Patents

Abstract

<PICT:0342651/IV/1> <PICT:0342651/IV/2> Artificial filaments, threads, ribbons, &c. of fine denier or of increased strength are formed by wet spinning a solution so as to form products having a skin-like outer layer, then subjecting such products to the action of a softening agent and stretching and completing the setting of the products. For viscose and cupraammonium solutions a coagulating bath of appropriate length and/or concentration is employed to obtain the formation of the skin. After leaving the coagulating-bath the filaments &c. are subjected to the action of a solvent or softening liquid such as zinc chloride, Schweitzer's reagent, ammonium sodium or calcium thiocyanate, &c. the liquid being contained in a bath or trough or applied as a spray or by rollers, rods or wicks. The filaments &c. may be washed before applying the softening treatment. Stretch may be applied to the softened filaments &c. by a roller having a peripheral speed greater than the speed of extrusion such roller being preferably of conical form to enable stretch to be imparted gradually. To complete the setting of the filaments &c., they are passed through a further coagulating-bath, which may be acid or alkaline. By confining the stretch wholly or partly to the softened portion, the products are further increased in strength; a roller, guide or tension device may be employed for this purpose, e.g. a roller rotating at a peripheral speed equal to or greater than the speed of extrusion or a gate-tension device comprising polished steel bars adapted to intermesh. The stretch-confining means may be combined with the softening-means, e.g. stretch may be restricted by passage of the filaments &c. over one or more wicks applying the softener. For nitrocellulose and cellulose acetate or other organic derivative of cellulose such as cellulose formate, propionate, butyrate or methyl, ethyl or benzyl cellulose, the skin is similarly formed and the products are softened by agents such as alcohol ether, amyl acetate, acetone, alone or mixed with alcohol or water, acetic acid, formic acid, lactic acid, acetyl acetone, dimethyl ethylene glycol, monomethyl ethylene glycol, monoethylene glycol, dioxane diacetone alcohol, methyl or ethyl lactate and mixtures thereof, the softening-agent being applied in liquid or vapour form; the completion of the softened and stretched products is effected either by the dry or evaporative method or by the wet coagulation method. Fig. 1 illustrates the method involving a softening liquid and further coagulating bath. The solution is extruded through a nozzle 3 into a bath 4 of about 4-6 inches and the partly coagulated filament is led over a roller 5 rotating at a speed of 40-50 metres per minute and sprayed with softening-liquid; the filament then passes through a second coagulating-bath 6 of 6-10 inches length and over a conical feed roller 7 into a centrifugal spinning-box 8. The roller 7 has a peripheral speed of 60-100 metres per minute. To confine the stretch to the softened portion, the filament passes around smooth glass rods 9, 11 carried by arms 12 and a rod 10 fixed in relation to the bath 6. Similar apparatus may be employed with a bath such as 6 for the softening liquid and a further setting-bath. For viscose, the baths 4 and 6 may be composed of 7,5 per cent sulphuric acid, 14,5 per cent sodium sulphate, 12 per cent glucose and 66 per cent water; the softening liquid may consist of a concentrated solution of zinc chloride or sodium or calcium thiocyanate. For a 20-20 per cent solution of cellulose acetate in acetone, the baths 4, 6 consist of a 10-12 per cent aqueous solution of diacetone alcohol or of methyl or ethyl lactate; and the softening-liquid comprises 70 per cent acetone or 50 per cent alcoholic acetone. As shown in Fig. 2, a 20-26 per cent acetate solution is spun through a short coagulating-bath 15 and the filaments then pass into a cell 16 having a lower compartment 19 through which solvent or softening vapours are circulated by a perforated supply ring 20 and an exit 26, and an upper compartment 21 in which the filaments are set by evaporative medium entering at 23 and leaving at 24 and heated by pipes 22. The filaments are drawn through the cell by a roller 17 and stretch is restricted by passing around smooth bars 27. The filaments pass to a cap-spinning device 18.